I'll preface this post by stating that in no way am I intending to trivialize the duties of any specific role within a film crew. Frankly, I've never worked on a project large enough to have dedicated DP, camera operator, and 1st AC positions, so perhaps it's not even my place to bring up this question...but I'll give it a try anyway Anyway, in the pecking order of a film crew, the camera operator typically works under direction of the DP, and the 1st AC works under the camera operator. Could it be argued, though, that despite this hierarchy, in some respects the 1st AC has a greater responsibility and requires more technical skill than a camera operator?
Granted, there's certainly a degree of skill involved in being a good camera operator, but from a creative perspective, camera operators typically take their cues from the DP. From a technical perspective, it seems that most responsibility is in the hands of the 1st AC. Making sure aperture, shutter angle, and shutter speed are all set properly? That's up to the 1st AC. Pulling focus, especially for tricky shots with fast motion and/or very shallow DOF? Again, that's all on the 1st AC.
Perhaps I'm way off on this argument. Maybe it simply comes down to the fact that there are creative and technical aspects of every production and a camera operator's duties tend to be more creative in nature, while the AC caters to the more technical side of production, and it takes both working together to end up with a quality product in the can. Still, I'd be interested to hear others' thoughts on this.